Downlink power control is usually used for limiting interference in a system so as to reduce intra- and intercell interference level, reduce consumption of transmission power of a base station, and ensure service quality of a user equipment. Power control of a physical layer usually consists of inner loop power control and outer loop power control.
Referring to FIG. 1, in control of transmission power of a base station for downlink signal, a closed-loop power control mode may be used. In this control mode, the power control includes inner-loop power control 1 and outer-loop power control 2. The outer-loop power control 2 aims to obtain a real-time updated target value (e.g., a target signal-to-inference ratio or signal-to-noise ratio) for signal quality by comparing the monitored actual signal quality (which may e.g. be a statistic value of a block error rate) with the target signal quality (which may e.g. be a target block error rate) desired for services, and allocate the target value to an inner-loop power control process for the inner-loop power control. The inner-loop power control 1 may predict signal quality of a next subframe according to the signal quality currently measured (e.g., the signal-to-interference ratio or the signal-to-noise ratio) and the past several measured values for the signal quality, obtain a power control command concerning power adjustment by comparing a predicted value of the signal quality with the target value of the signal quality provided by the outer-loop power control, and transmit the power control command to the base station via an uplink signal. The base station typically regulates transmission power of the downlink signal according to the power control command.
Considering a weak signal scenario, e.g., when a user equipment (UE) is located at an edge of a cell, a target signal-to-interference ratio of the UE may be continuously increased, even to or beyond a maximum permissible value (at this time, the base station may transmit a signal to the UE at a maximum transmission power). During this process, there is no obvious improvement on demodulation performance of the signals received by the UE. When the UE moves towards the base station, the channel environment is improved. However, limited to a longer adjustment cycle and a smaller adjustment step of the outer loop, the UE will take many subframes so as to gradually adjust the target signal-to-interference ratio to an appropriate level. During a period of these subframes, usually signal transmission power of the base station is obviously greater than a proper level, and as a result, strong interference is brought to the other UEs (User Equipments) working at the same cell. This phenomenon is usually called as windup effect.